The present invention relates to docks and boat lifts and more particularly to floatable and pneumatically operable docks and boat lifts.
It is the practice, particularly in inland lakes in northern climates, to erect or install boat docks and boat lifts into the lake during the early spring, and to remove these items at the end of the summer and before lake freeze-up. In the case of some boat docks, it is necessary to wholly or partially dismantle the dock at the time it is removed from the lake, and to reassemble the dock during the spring when it is replaced into the lake. It has become a common practice to construct docks in sections, so that assembly and disassembly can be accomplished by one or two people with a minimum of inconvenience. Boat lifts, on the other hand, are typically constructed from a network of frame members which is made as lightweight as practical, so as to facilitate easy removal and replacement of the entire framework. The framework may be constructed so as to have skids on the bottom of its legs, to thereby make the task of removal and replacement easier.
It would be an advantage if such devices could be constructed so as to be conveniently moved in and out of position relative to the water, and more particularly, it would be an advantage if such devices could be merely floated into position and thereafter sunk into the lake bed; upon removal from the lake it would be an advantage if such devices could be refloated for purposes of removal. The prior art exemplifies a number of attempts which have been made to accommodate this problem, as illustrated in the following paragraphs.
The Rogers U.S. Pat. No. 2,151,394, issued Mar. 21, 1939 and entitled "Boat's Drydock," discloses a fluid-operated raising and lowering plunger vertically disposed within a fluid cylinder countersunk in a bed. Pipes deliver and discharge fluid under pressure to and from the cylinder for operation of the plunger. A cradle is fixed to the upper end of the plunger to accommodate a ship.
The Henderson U.S. Pat. No. 3,537,412, issued Nov. 3, 1970 and entitled "Stabilizer for Marine Vessels," discloses a set of buoy pipes to be secured on each side and each end of a vessel. The pipes project downwardly into water beyond the draft of the vessel. The lower end of the pipes are open while the upper end is closed. Air is pumped into the buoy pipes to displace water therefrom. The air pressure within the pipes generates an upward force to pneumatically jack the vessel above the water's surface.
The Garrison U.S. Pat. No. 3,648,314, issued Mar. 14, 1972, entitled "Self-Stabilizing Flotation Module," discloses a module having open-bottomed containers from which liquid is displaced by gas for lifting submerged material. In operation, the module may be placed in the water and submerged by venting entrapped gas. At the desired location, it may be attached to an object, and the water within the containers displaced by gas.
The Rutter U.S. Pat. No. 4,018,179, issued Apr. 19, 1977, and entitled "Pontoon System for Supporting Watercraft on a Body of Water," discloses a submersible structure comprised of pontoons into which air is injected, expelling the water therefrom to provide lift for lighter and heavier portions of the structure. The structure includes support pads which contact the hull and keel of a water craft. Air may be released from the pontoons for lowering the structure into the water.
The Wells U.S. Pat. No. 4,280,429, issued July 28, 1981, and entitled "Floating Boat Storage Dry Dock," discloses a tubular, boat-supporting platform made from a planar array of interconnected conduit and a pair of vertical, buoyant, tubular sidewalls connected to the platform. Water is pumped into and out of the platform tubular array to control the depth level of the platform. The vertical sidewall conduits are filled with air to add positive buoyancy to the platform.
Boat lifts for runabouts, fishing boats, sailboats, and the like are widely commercially available in many sizes and configurations. Such boat lifts usually have a cabling system, a self-braking winch, adjustable leveling legs, and rear cradles that adjust vertically and horizontally to support a boat.
Commercially available boat lifts are allegedly portable, but they frequently weigh from 300 to 1,000 pounds and have beam widths ranging from five to ten feet. Moreover, although they may be "portable" by being arguably attachable to a trailer, the lifts themselves have no transportation means such as wheels. Even if a lift of the type available is transported on a trailer which is driven into a lake, depositing of the lift typically requires at least a four-man operation, especially for a massive boat lift. Situating the lift also requires wading into the water, and a diving operation to adjust the height of the boat lift. Such efforts must be expended for each change of location of the boat lift.